I have 2 Deco XE75, both worked perfectly but suddenly, the secondary one started disconnecting (changing from green to red to yellow to green) i tried resetting both, but to no avail

Nice to meet you, *****!

Does only one Deco have this problem?

Have you tried swapping them?

That is, after you swapped them, the first one stopped working
Oh, got it

Can ask you to put them next to each other
Let's see if they work well

Both?

Then most likely the problem is that the stations were far from each other or something in the place where you had the 2nd station jams the signal

Factory reset the device and set it up again from scratch

Here are the steps to perform a factory reset on a TP-Link Deco device:

1. Locate the reset button on the device. It is usually a small button located at the bottom or back of the
   device.
2. Press and hold the reset button for 10 seconds or until the LED light on the device starts flashing.
3. Release the button and wait for the device to restart.
4. 
   Set up the device again from scratch using the TP-Link Deco app.

You can use an extension cable to relocate the modem to a better location.

The device may lost the connection, that's why it may stop working suddenly.
Don't worry, just follow the instructions below in order to fix this issue:

1. Locate the reset button on the device. It is usually a small button located at the bottom or back of the device.
2. Press and hold the reset button for 10 seconds or until the LED light on the device starts flashing.
3. Release the button and wait for the device to restart.
4. Set up the device again from scratch using the TP-Link Deco app.
   In addition, you can use an extension cable to relocate the modem to a better location.

Is there anything else I can do for you today?